1. Today4/10 Current Loops HW: 4/10 “Force on Loops” Due Monday, 4/14
“Phantom” magnets
Force/torque on loops in a B-field
HW: 4/10 “Force on Loops” Due Monday, 4/14

2. B Fields - Current Loop
Current loops

3. B Fields - Magnet Current loops are magnets!!! Behave like magnets!!!

4. B Fields - Current Loop
Current loops
Phantom Bar Magnet N S

5. Magnetic Torque, Loops What happens to loop?
Turn the loop into a magnet. Magnets line up with the field. (A compass needle is a magnet!)
Loop is a magnet (needle) centered in the loop with the N pole facing away from you. S
The loop (magnet) will rotate so it lines up with the field. (S up and out of the page)

6. Magnetic Torque, Loops What happens to loop?
Turn the loop into a magnet. Magnets line up with the field. (A compass needle is a magnet!)
Loop is a magnet (needle) centered in the loop with the N pole facing away from you. S N
The loop (magnet) will rotate so it lines up with the field. (S up and out of the page)
This is a torque on the loop.

7. Clockwise (viewed from above) 90° North out
A bar magnet and current loop (powered by a battery) are shown in various orientations below. In each case the magnet if held in place and the current loop is released and allowed to rotate only about the axis shown. Determine if the loop will rotate. If so, find the direction of rotation and how far it rotates. If the loop is in unstable equilibrium, say so. (RHR #3) N S
Clockwise (viewed from above) 90° North out N S
Torque clockwise from above, can’t turn North out N S N S
Clockwise (viewed from above) 90° North in
Unstable equilibrium small tap will cause a 180° flip either direction. North right

8. Magnetic Force, Loops What happens to loop?
Turn the loop into a magnet. Like poles repel.
real magnet
Loop is a magnet (needle) centered in the loop with the N pole facing away from you. N S
Unlike poles attract so the loop is attracted, force on loop is to the left.

9. Magnetic Force, Loops What happens to loop?
Turn the loop into a magnet. Like poles repel.
real magnet
Loop is a magnet with the N pole facing left S N S N
Like poles repel so the loop is repelled, force on loop is to the right.